Abstract: An abnormality determination unit that determines whether or not an output measurement unit is abnormal is provided, and whether or not the output measurement unit is abnormal is determined. When the output measurement unit is abnormal, an elastic actuator is controlled based on a desired internal state decision unit and an internal state error compensation unit. Accordingly, it becomes possible to control the elastic actuator to continuously operate to a predetermined position without instantaneously stopping even when the output measurement unit is abnormal.

Abstract: A method for determining gain of a back-electromotive force amplifier may include setting an electric motor into a tri-state function mode and storing a first quasi steady-state value for back-electromotive force from the difference signal, and forcing a reference current through the electric motor and determining a first value of the gain of the amplifier for equaling a difference signal to the first quasi steady-state value. The method may further include setting the electric motor into a tri-state function mode a second time and storing a second quasi steady-state value for back-electromotive force from the difference signal, and increasing the first value of the gain by an amount proportional to a difference between the second quasi steady-state value and the first quasi steady-state value.

Abstract: In accordance to an aspect of the disclosed embodiments, a substrate transport apparatus is provided. The substrate transport apparatus includes a frame defining a chamber, at least one stator module embedded at least partly into a peripheral wall of the chamber, the at least one stator module defining an axis of rotation. The substrate transport apparatus further includes at least one rotor substantially concentrically disposed relative to the at least one stator module about the axis of rotation, the at least one rotor being configured to interface with the at least one stator module and being suspended by a respective one of the at least one stator module substantially without contact within the chamber. The substrate transport apparatus further includes at least one substrate transport arm connected to the at least one rotor and having at least one end effector configured to hold at least one substrate.

Abstract: A motor control system includes a motor unit and a controller unit electrically connected therewith. The motor unit includes a motor, a resolver detecting a rotational angle of the motor and a first memory storing first error data for detection by the resolver of the motor's rotational angle. The controller unit includes a second memory storing second error data for detection by the resolver of the motor's rotational angle and a motor controller determining an actual rotational angle of the motor according to the detected rotational angle detected by the resolver and the second error data in the second memory and controls the motor's rotation according to the determined actual rotational angle. The motor unit or the controller unit further includes an update section updating the second error data with the first error data according to motor data in the first and second memories.

Abstract: A robust method for detecting a relative position of a feedback device, such as an encoder or resolver, coupled to a shaft, such as a motor shaft, is provided. To detect the relative position, electrical commands are issued in an open loop mode to spin the motor shaft an amount greater than the apparent rotational angle between two consecutive markers of the position feedback device, such that the net mechanical rotation is equal to or greater than the total rotational angle between two consecutive markers.

Abstract: The invention provides a driving circuit for a voice coil motor. In one embodiment, the driving circuit includes a logic circuit, a digital-to-analog converter, and an output circuit. The logic circuit generates a series of samples of a digital output signal according to a digital input signal, wherein the samples of the digital output signal sequentially alter from a first input value of the digital input value to a second input value of the digital input signal according to an alteration pattern determined by a mode selection signal. The digital-to-analog converter converts the digital output signal to an analog output signal. The output circuit generates a driving current signal according to the analog output signal for driving the voice coil motor.

Abstract: A motor controller capable of detecting an oscillation of a feedback loop and performing gain adjustment while updating a gain value of a control unit is provided. The motor controller includes an electric motor, an operation-amount detector, a control unit, a machine, a disturbance signal generator which generates a sweep sine wave, a compensation-driving-force detector, a vibration calculator, an oscillation detector, a vibration storage, a simulated open-loop gain calculator, a gain changer, and an automatic gain changer, and detects an oscillation by processing a response signal in time series on the basis of a first threshold regarding to a magnitude of vibration and a second threshold regarding a frequency.

Abstract: A sampling circuit samples, while running a motor at a predetermined rotational speed, over a predetermined period a back electro-motive force induced at one end of at least one phase coil, with one end of each phase coil of the motor being brought to a high impedance. A waveform data generating circuit holds as waveform data SIN the back electro-motive force beforehand sampled by the sampling circuit. A PWM signal generating circuit sequentially reads the waveform data SIN from the waveform data generating circuit to generate a PWM signal Spwm, the pulse width of which is modulated.

Abstract: A machine tool is fitted with a position detector for detecting a position of a moving axis of the machine tool and an on-machine measuring device for measurement on the machine tool. An axial position detection signal output from the position detector and a measurement signal output from the on-machine measuring device are received through interfaces by a numerical controller that controls the machine tool. These interfaces are designed so that the numerical controller receives the axial position detection signal and the measurement signal with the same timing.

Abstract: A method is provided for adapting controller parameters of a drive to different operating states. A control loop includes a PID controller whose I gain factor is adapted to a drive velocity and/or whose D gain factor is adapted to a drive current, and consequently to a drive load. The I gain factor is determined based on the drive velocity and the D gain factor is determined based on the drive current, in each case at least in one area, the I gain factor falling with the drive velocity and the D gain factor rising with the drive current.

Abstract: A filter representing a complex impedance of a motor system based on a deviation between a first voltage driven by a command signal and a second voltage driven by the command signal can be dynamically adjusted. The motor system can be held in a steady state, eliminating back electromotive force, by providing zero mean current excitation.

Abstract: A system and method for setting machine limits include setting a limit for a machine parameter, setting a temporal operating range for the machine, and setting a temporal step. The machine is operated over the operating range and the machine parameter is measured. A first new limit for the machine parameter is set based at least in part on the measurements over the operating range. The operating range is advanced by the temporal step, and the machine parameter continues to be measured. Another new limit for the machine parameter is set based at least in part on the measurements over the operating range after the operating range has been advanced.

Abstract: A method and a system for video camera assembly are provided. The video camera assembly includes at least one of a pan mechanism rotatable about a pan axis and a tilt mechanism rotatable about a tilt axis. The pan mechanism includes a pan motor and a pan position encoder. The tilt mechanism includes a tilt motor and a tilt position encoder. A controller is communicatively coupled to at least one of the pan mechanism and the tilt mechanism and is configured to apply a filter to a power drive signal of at least one of the pan motor and the tilt motor based on a determined corresponding rotational speed of the at least one of the pan motor and the tilt motor with the effect of reducing steady state vibrations which degrade the visual and audible qualities of said video camera assembly.

Abstract: A positioning device includes a driver which moves a positioning object and a sensor which measures the distance to the positioning object in a non-contacting manner and outputs a detection signal if the positioning object is detected only in a length measuring area within a predetermined range from any detection position, shaft controller which stops the driver by detecting the detection signal from the sensor and automatically correcting for an overshoot amount between the stop position and any detection position, when the driver moves the positioning object and the sensor, and the positioning controller that stores the coordinate value after the automatic correction by the shaft controller and that performs the positioning based on the reference coordinate value.

Abstract: This invention relates to a servo system for operating an exoskeleton adapted to encircle an object of interest and for supplying a force thereon. A servomotor is coupled to a power source and operates the position of the exoskeleton and thus the force exerted by the exoskeleton on the object of interest. A measuring unit measures a raw driving current signal Iraw supplied by the power source to drive the servomotor. A low pass filter applies a low pass frequency filtering on the measured a filtered current signal Ifiltered. A processing unit determines an actuated current signal Iactuated based on the servomotor setting parameters, where Iactuated indicates the contribution to Iraw from the servomotor when operating the position of the exoskeleton. The processing unit also determines a driving force current signal Iforce indicating the force exerted by the exoskeleton on the object of interest, where Iforce is proportional to the difference between Ifiltered and Iactuated.

Abstract: A system and method of modeling, prediction, optimization and controlling an embedded alarm control having a plurality of independently controlled, manipulated variables, at least one controlled variables and one or more disturbance variables. The method includes determining simultaneously a set number of dynamic moves of the manipulated variables along with steady state values of the manipulated and controlled variables with steady state constraints relating to the manipulated and controlled variables as well as dynamic constraints relating to the manipulated and controlled variables including relating to the disturbance variables. Embedding alarm controls in the simultaneous dynamic control and steady state optimization with varying type of alarming situations and aiding operator in recovery actions.

Abstract: A method, computer readable medium, and apparatus for controlling a moveable element includes generating and providing with a control device one or more driving signals to one or more positioning actuators to move the moveable element towards a target position based on a target travel distance and a calibration value. The control device determines when a post-movement position of the moveable element is outside of a tolerance range of the target position. The control device recalibrates the calibration value when the post-movement position is determined to be outside of the tolerance range. The control device repeats the generating, the determining, and the recalibrating as open loop steps until the post-movement position is within the tolerance range or until a limit, if any, on attempts is reached.

Abstract: In a method for reliably monitoring the speed of a moveable coordinate measuring device, a first value of the speed is calculated from measured values of the coordinate measurement system. The measured values contain information on positions of the coordinate measuring device. The measured values are further used to determine the coordinates of a measurement object. A second value of the speed is ascertained from measurement signals of at least one additional movement sensor. The measurement signals can also be used for controlling a drive device of the coordinate measuring device. A fault signal can be generated if the first value and/or the second value deviate from one another, from a predetermined value and/or a limit value according to a predefined criterion.

Abstract: A device-positioning pedestal capable of positioning devices of different sizes. The device-positioning pedestal comprises a plurality of guide members corresponding to the sides of the device and coming in contact with the sides of the device to position the device, at least one guide member includes a slide mechanism that supports the guide member so as to slide relative to the device-positioning pedestal member and a fixing mechanism that fixes the guide members at desired positions. The guide members are set to be adapted to the size of the device by the guide member-adjusting means separate from the device-positioning pedestal. The guide member-adjusting means adjust the position of the guide members based on the size of the device measured by device size-measuring means separate from the guide member-adjusting means or based on the data of data-recording means attached to the device-positioning pedestal.

Abstract: A motion control servo loop apparatus, comprising: a feed-forward control module, and a proportional-integral-derivative (PID) control loop and a compensation adder. The feed-forward control module is capable of generating a feed-forward compensation. The PID control loop further comprises: a proportional control module, an integral control module and a derivative control module. The proportional control module is capable of generating a proportional compensation. The derivative control module is capable of generating a derivative compensation. The integral control module uses a digital differential analyzer (DDA) algorithm to perform integration for accumulated errors with respect to each sampling clock at each DDA pulse and thus output an accumulated error, which is then processed to generate an integral compensation.

Abstract: An HVAC actuator, such as a spring return actuator, may adjust the maximum output torque of the motor with the varying spring return force of the HVAC actuator as the HVAC actuator moves through its range of motion. In some cases, this may provide a more constant force at the output of the HVAC actuator and reduce the force that is applied through the motor, drive train and/or the HVAC component when an end stop is reached. Also, an HVAC actuator is disclosed that can be configured to discover and store the location of one or more end stop(s), and to slow the speed of the motor down before the end stop(s) is reached. This may reduce the force that is applied through the motor, drive train and/or the HVAC component when an end stop is reached.

Abstract: A driving apparatus has a correction value output unit for outputting correction values ?Ta and ?Tb to correct differences between signals which are output from an A sensor a B sensor when an A-phase coil and a B-phase coil are not energized and signals which are output from the A sensor and the B sensor when the A-phase coil and the B-phase coil are energized. An energization direction of the A-phase coil is switched on the basis of a time A which is measured by a time measurement unit and the correction value ?Ta which is output from the correction value output unit. An energization direction of the B-phase coil is switched on the basis of a time B which is measured by the time measurement unit and the correction value ?Tb which is output from the correction value output unit.

Abstract: A method of adjusting operating parameters of a robot to move an effector tool along a given path in an optimum cycle time including a step of modifying operating parameter values to cause the cycle time to approach a optimal value wherein the parameters are modified so as to approach an extremum of a compromise function including at least first and second terms, the first term being a function of a cycle time and the second term being a function of at least one of temperature and degree of wear of an actuator.

Abstract: Disclosed are various systems and methods for assessing and improving the capability of a machine tool. The disclosure applies to machine tools having at least one slide configured to move along a motion axis. Various patterns of dynamic excitation commands are employed to drive the one or more slides, typically involving repetitive short distance displacements. A quantification of a measurable merit of machine tool response to the one or more patterns of dynamic excitation commands is typically derived for the machine tool. Examples of measurable merits of machine tool performance include workpiece surface finish, and the ability to generate chips of the desired length.

Abstract: Disclosed are various systems and methods for assessing and improving the capability of a machine tool. The disclosure applies to machine tools having at least one slide configured to move along a motion axis. Various patterns of dynamic excitation commands are employed to drive the one or more slides, typically involving repetitive short distance displacements. A quantification of a measurable merit of machine tool response to the one or more patterns of dynamic excitation commands is typically derived for the machine tool. Examples of measurable merits of machine tool performance include dynamic one axis positional accuracy of the machine tool, dynamic cross-axis stability of the machine tool, and dynamic multi-axis positional accuracy of the machine tool.

Abstract: Controller scaling and parameterization are described. Techniques that can be improved by employing the scaling and parameterization include, but are not limited to, controller design, tuning and optimization. The scaling and parameterization methods described here apply to transfer function based controllers, including PID controllers. The parameterization methods also applies to state feedback and state observer based controllers, as well as linear active disturbance rejection controllers.

Abstract: This document describes a correction signal usable to correct an effect of a disturbance signal on a controlled system or apparatus. In one case this document describes ways in which to diminish a future change to an output signal based on determining that a disturbance signal consistently precedes the future change.

Abstract: A control device for a machine tool including a feed axis driving motor; a first power consumption calculating portion calculating power consumption of the feed axis driving motor; a second power consumption calculating portion calculating power consumption of equipment adapted to be operated by constant power; and a motor control portion determining a target time constant correlated with at least one of acceleration time and deceleration time of the feed axis driving motor, based on a summation of the power consumption calculated by the first power consumption calculating portion and the power consumption calculated by the second power consumption calculating portion, and controlling the feed axis driving motor based on the target time constant.

Abstract: A flux switching electric motor (102) is disclosed. The motor comprises a rotor (104), a stator (106), field windings (124, 126) and armature windings (128, 130). #A microcontroller (134) controls supply of electrical current to the field and armature windings. A rotor position sensor includes a divider for (i) receiving an input signal dependent upon the rate of change of current in at least one field winding, (ii) receiving an input signal dependent upon the voltage across at least one armature winding, current through which causes at least part of the current in the field winding, and (iii) providing the microcontroller (134) with a control signal which is dependent upon the ratio of the input signals received by the divider.

Abstract: A substrate transport apparatus including a peripheral wall having an inner surface that defines a substrate transport chamber capable of holding an isolated atmosphere, at least one substantially ring shaped motor having at least one stator module located within the peripheral wall, between the inner surface and an adjacent outer surface of the peripheral wall and at least one rotor suspended substantially without contact within the transport chamber such that a surface of the peripheral wall encompassed by the ring shaped motor is configured for attachment thereto of a predetermined device and at least one substrate transport arm connected to the at least one rotor and having at least one end effector configured to hold at least one substrate.

Abstract: A disclosed servo control device includes a servo control unit configured to control a driving unit for driving a driven body with servo control, and a changing unit configured to change a timing of ending the servo control in response to stop position accuracy for a target stop position of the driven body when the driven body is driven to move, wherein the servo control unit detects an error between the target stop position and an actual stop position of the driven body, and corrects the timing of ending the servo control using the detected error.

Abstract: At an initial drive operation after turning on of an electric power source, an ECU sequentially changes each current exciting phase among multiple phases through one complete cycle at a predetermined time schedule, so that a rotational position of a rotor and the corresponding exciting phase coincide with each other at some timing during the initial drive operation, and thereby the rotor is rotated. The ECU counts the A-phase signal and the B-phase signal during the rotation of the rotor in the initial drive operation and learns a relationship among a count value of the A-phase signal and the B-phase signal, a rotational position of the rotor and each exciting one of the plurality of phases at an end of the initial drive operation. When the ECU determines that a result of the learning is erroneous, the ECU re-executes the learning by re-executing the initial drive operation.

Abstract: A machine tool includes a time calculation unit calculating the time for a spindle to arrive at a target rotational speed, and the time for a spindle head to arrive at a target position; a comparison unit comparing the time to arrive at the target rotational speed and the time to arrive at the target position; and a drive control unit controlling the drive of the spindle and the drive of the spindle head. The drive control unit controls the drive of the spindle head, when a determination is made that the time to arrive at the target rotational speed is longer than the time to arrive at the target position, such that the time for the spindle head to arrive at the target position is longer than the calculated time to arrive at the target position, and less than or equal to the calculated time to arrive at the target rotational speed. Accordingly, the machine tool can drive the spindle head that is a control object in a power-saving mode.

Abstract: Described is a fault-tolerant electro-mechanical system that is able to saccade to a target by training and using a signal processing technique. The invention enables tracking systems, such as next generational cameras, to be developed for autonomous platforms and surveillance systems where environment conditions are unpredictable. The invention includes at least one sensor configured to relay a signal containing positional information of a stimulus. At least one actuator is configured to manipulate the sensor to enable the sensor to track the stimulus. A processing device is configured to receive positional information from each sensor and each actuator. The processing device sends a positional changing signal to at least one actuator and adjusts at least one positional changing signal according to the information from each sensor and each actuator to enable the actuator to cause the sensor to track the stimulus.

Abstract: A control system having an integrator component that provides an integrator output signal used to control a load, and a method controlling the same includes conditioning the integrator component during a fraction of the period in which it would tend to otherwise wind-up.

Abstract: A servomotor control system that includes a numerical control unit and servo control unit enables the use of learning control based on an angle synchronization method in high-speed oscillating motion performed by, for example, a jig grinder. The numerical control unit calculates a reference angle ?(=?t), and also calculates a cyclic oscillation command F(t) according to the reference angle ? and a machining condition (angular velocity ?). The servo control unit calculates a difference between the value in the oscillation command F(t) and the position of the servomotor (positional difference ?) at intervals of a predetermined cycle, and performs learning control according to the reference angle ?, oscillation command F(t), and positional difference ?.

Abstract: A method and system of determining tuning parameters for use in tuning a controller used in a process control loop for a motor and associated load. The method includes providing tuning parameters, applying an excitation test signal, receiving frequency response data to determine phase and gain margins, creating an instability region defined by a bounded area that connects the phase and gain margins with a boundary on a gain vs. phase plot, assigning and applying cost functions, and computing stability determinations.

Abstract: Embodiments of the invention provide a fire-extinguishing system and method for injecting foamant into a stream of water. The system can include a flow meter determining a flow rate of the stream of water and a foam pump having an inlet coupled to a supply of foamant and an outlet coupled to the stream of water. The system includes a servo motor driving the foam pump. The servo motor includes a sensor used to determine a rotor shaft speed and/or a rotor shaft torque.

Abstract: Disk drive spindle jitter is comprised of electrical noise, error due to pair pole asymmetry, and random disk speed variances. Error caused by pair pole asymmetry can be identified and compensated for by detecting over a single rotation of a rotor a plurality of zero cross signals. These signals can be statistically analyzed over a period of a plurality of revolutions of the rotor so as to identify the systematic error caused by pair poles. Once identified, this pair pole error can be used to modify zero cross signals and/or modify commutation signal driving the disk so as to arrive at a more accurate determination of disk speed and to precisely control the speed of the disk.

Abstract: A driving apparatus (100p, 100s) is provided with: a base portion (110); a stage portion (130) on which a driven object (12) is mounted and which can be displaced; an elastic portion (120) which has elasticity to displace the stage portion in one direction (Y axis); a first applying device (151-2, 152-2, 22) for applying an excitation force for displacing the stage portion such that the stage portion is resonated in the one direction at a resonance frequency determined by the stage portion and the elastic portion; and a second applying device (151-1, 152-1, 22) for applying a driving force for displacing, in a stepwise manner or in a continuous manner, the stage portion or the driven object mounted on the stage portion in other direction (X axis), wherein the stage portion or another stage portion mounted on the stage portion as the driven object is divided into a plurality of stage fractions.

Abstract: An apparatus including a DC motor includes a driven member configured to be driven by the DC motor, and a drive control unit configured to define a plurality of predetermined phases of the DC motor as target stop phases and to cause the DC motor to make at least one rotation to perform preliminary driving that rotates the DC motor to each target stop phase by driving and stopping the DC motor, configured to acquire a difference value between the target stop phase and an actual stop phase for each target stop phase, and configured to drive the DC motor so that the driven member is repeatedly moved and stopped in the operation of the driven member and to perform control so that, based on the difference value acquired by the acquisition unit, electric power is supplied to the DC motor in a phase corresponding to a stop position of the driven member.

Abstract: A method for controlling the kinematics of a seat (10) having movable portions (16, 18, 20, 22) and actuators (24, 25, 26, 27) for moving the movable portions between an initial position and a final position, at least one movable portion including a specific point (P1, P2, P3, P4), includes the steps of: establishing (102), for the specific point, an authorized travel conduit (C) between the initial position and the final position, delimited by two lateral boundaries (Z1, Z2); calculating (116) the current position of the specific point; establishing (118) a target direction for the specific point that is suitable for moving the specific point in the conduit (C) from the lateral boundaries and the current position; and modifying (122) the direction of the specific point by controlling the actuators in order to force the specific point to move in the conduit (C).

Abstract: A motion-control system includes an operator interface with an operator-input member and a controllable force feedback device drivingly connected to the operator-input member. The motion-control system may also include controls that regulate the motion of one or more moveable components, including adjusting a first operating parameter in a manner that depends at least in part on a control error between a target value of a second operating parameter and an actual value of the second operating parameter. The target value of the second operating parameter may be based at least in part on the motion of the operator-input member. The controls may also operate the controllable force feedback device to provide feedback force on the operator-input member in a manner that depends at least in part on the control error and such that the derivative of the feedback force with respect to the control error varies dependent at least in part on the control error.

Abstract: Method for the automated startup and/or for the automated operation of controllers of an electrical drive system with vibrational mechanics with the following steps: Determination of a preliminary value of at least one parameter, Determination of a model of the electrical drive system by means of the determination of initially a non-parameterized model through the recording of frequency data during operation of the drive system subject to the utilization of the preliminary value of at least one parameter and the subsequent determination of parameters of the electrical drive system based on the frequency data and subject to the optimization of at least one preliminary value of at least one parameter by means of a numerical optimization method on the basis of the Levenberg-Marquardt algorithm and Parameterization of the plurality of or at least one controller of the electrical drive system by means of at least one of the determined parameters.

Abstract: A drive control apparatus includes: a first feed-forward control unit which obtains a first feed-forward signal by applying a first perfect tracking control method to a first transfer function which shows a portion of an inverse system of transfer characteristics of a control subject; a second feed-forward control unit which obtains a second feed-forward signal by applying a second perfect tracking control method to a second transfer function which shows a portion of an inverse system of transfer characteristics of the control subject and which is different from the first transfer function; and an external disturbance observer which obtains a first compensation signal for the first feed-forward signal, wherein the control subject is driven using a second compensation signal which is obtained from the second feed-forward signal and the first compensation signal.

Abstract: A servo control apparatus that performs dual-position feedback control and thereby achieves a reduction in position error according to the purpose of machining.

Abstract: A servomotor controller capable of properly generating reference positions, by which learning control of angle based method may be applied to the periodically reciprocating motion of an object. The learning controller obtains a first positional deviation of a driven object at every predetermined sampling period of time, and the first positional deviation is converted, by a first converting part, to a second positional deviation associated with each reference position in one periodic reciprocating motion of the driven object. After a first correction amount of an immediately previous reciprocating motion of the driven object, stored in a memory, is added to the second positional deviation, the second positional deviation is stored in the memory as a renewed first correction amount. The first correction amount is converted to a second correction amount associated with the sampling period, by a second converting part.

Abstract: A control system includes a basic control command operating unit, a fuel data storage unit, a running results database for storing past running results values of a control subject, a data creating unit configured to calculate a distance between data of the past running results values and the data sets and determining data set in which a distance between data becomes minimum, a modeling unit configured to model a relationship between operation parameters of a combustion apparatus and components in combustion gas of the combustion apparatus by using the data set determined by the data creating unit and a correcting unit for calculating combustion apparatus operation parameters with which components having a better condition than that of the components in a current gas are provided by using a model of the modeling unit and correcting operation command values of the basic control command operating unit by calculated operation parameters.

Abstract: A method of power tuning an electric system, the electric system including an electric machine and a control system for driving the electric machine in response to control values stored in a power map. The method includes loading the control system with a first power map, driving the electric machine with the control system, measuring a power of the electric system, and loading the control system with a second power map in the event that the measured power lies outside a predetermined range.

Abstract: A mechanism for empirically deriving the values of the damping ratio and frequency of the mechanism driven by a servo-controlled control system is disclosed. In accordance with the illustrative embodiment, the values of the damping ratio and frequency are continually re-generated based on empirical data derived from sensor feedback of the maximum-amplitude switch and the linear second-order servo. Because the values of the damping ratio and frequency are generated from empirical data, it is not necessary that they be known, and because the values of the damping ratio and frequency are continually re-generated, variances in their values are continually noticed and compensated for.